72 LESSON XI. 



interesting, from the remarkable difference in the 

 appearance of the same shell at the various stages 

 of its growth. In its earliest state, the substance 

 of the shell is ve*ry thin, almost colourless, and 

 dull ; the mouth rather wide, the outer lip not 

 rolled inwards, but having a sharp edge, and 

 neither lip denticulated. The shell which the 

 animal first forms is so dissimilar to the perfect 

 Cypraea, that it has been considered as belong- 

 ing to another genus. In the second, or inter- 

 mediate period of growth, the shell begins to 

 approach the general form that characterizes the 

 genus. The lips are curved inwards, and the 

 teeth become apparent ; but the substance is still 

 thin, the colour faint, and the markings seldom 

 more than ill-defined transverse bands. In its 

 third and perfect state, the Cypraea has received 

 an additional coating of testaceous matter, the 

 pattern appears with its vivid tints and delicate 

 markings, and the spire, if not entirely hidden, 

 yet scarcely projects out of the body whorl. 

 The animal itself undergoes a considerable 

 change in appearance during its growth ; its 

 mantle at first is small, but increases with its age, 

 and expands at the sides into two ample wings ; 

 from these is deposited the final layer which 

 completes the shell. 



In the adult specimens, these expansions of 

 the mantle completely cover the shell, when the 

 animal emerges to seek its food ; at the place 

 where they unite, a longitudinal line is formed 

 on the back of the shell, thence called the dorsal* 



.Dorsal, belonging to the back, from the Latin'ciorswwi the back. 



